1. Field of the Invention
The invention relates to a mobile communication system, a control device thereof, a mobile terminal, and a database constructing method. The invention relates to an improvement of a mobile communication system forming radio zones, for example, in a macro cell system. Particularly, the invention relates to switch processing the base stations as the mobile terminal moves among the radio zones. For example, the switch processing is so called handover or handoff.
2. Description of the Related Art
Systems forming an area of a mobile communication system are broadly classified into macro cell systems and micro cell systems. A representative of the former is a so-called cellular phone system; the radius of each radio area is several km. Meanwhile, for example, a personal handy-phone system (PHS), as it is called in Japan, adopts the latter; its area radius is very small and is several hundred meters at maximum.
In the micro cell system, the number of base stations increases or decreases frequently in response to a change in the communication demand of a region. Accordingly, there is no real plan as regards the base stations (base station location design), as regards installation location and location relationship with adjacent base stations, and base stations are always installed spontaneously. The resulting interference among areas needs to be dealt with by each base station in order to avoid cross talk.
To perform handoff, a system of this kind has to switch areas in accordance with a re-calling operation from a mobile terminal. In the micro cell system, handoffs occur so frequently that the system is weak in high-speed movement of the mobile terminal, which has resulted in the need for increased resolution. However, under the present circumstances, the performance of the handoff depends heavily on the ability of the mobile terminal. Enhancing the high-speed moving performance increases the cost of the mobile terminal, which results in a heavy burden on the user, and thus requires resolving.
According to a technique which is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-211768, a mobile communication system may recognize an area in which a radio wave from a base station (referred to as a cell station) has a low intensity; however a system in which base station location design was not carried out cannot receive the full benefit of its effect.